Gas turbine engine rotor shaft bearing assemblies may be of the plain bearing type which are segmented (radially self-aligning), retained in an outer carrier, oil pressure lubricated and known as tilt pad bearings. Such bearings are subject to high speed and load when the engine is running and very small out of limit wear in a bearing can have disastrous effects on an engine. It may cause engine shut-down which, for this kind of engine, is usually a very costly matter. For acceptable engine life it is therefore vital that the bearings perform reliably.
It is typical in such segmented plain bearing arrangements to restrain circumferential movement of each segment by use of retaining pins which are fixed in the bearing assembly outer carrier and abut to segments either at segment end faces or at the side face of an internal hole or passage in the segment body. The pin may be a parallel round pin throughout its length, but a known variation is for a pin with spheroid tip on a round pin stem, the sphere diameter being greater than the round pin stem.
It has been found that at contact faces between the bearing segments and bearing outer carrier, fretting wear may occur which allows segments to move beyond design limits and thus cause bearing related engine problems. It is believed the fretting is caused by a small amount of circumferential sliding action under pressure between segment and carrier and that the action is made possible with prior art pin designs.